SIEMENS
SINAMICS S150 NEMA
Engineering Information
3
Siemens D21.7
(Part 2) – 2015
3/20
Safe Torque Off (STO)
The STO function is the most common and basic drive-
integrated safety function. It ensures that no torque-
generating energy can continue to affect a motor and
prevents unintentional startup.
Effect
This function is a mechanism that prevents the drive from
restarting unexpectedly, in accordance with EN 60204-1,
Section 5.4. Safe Torque Off suppresses the drive pulses
(corresponds to Stop Category 0 of EN 60204-1). The drive is
reliably torquefree. This state is monitored internally in
the drive.
Application
STO has the immediate effect that the drive cannot supply
any torque-generating energy. STO can be used wherever
the drive will naturally reach a standstill due to load torque
or friction in a sufficiently short time or when “coasting
down” of the drive will not have any relevance for safety.
Customer benefits
The benefit to the customer of using the Safety Integrated
function STO as opposed to a conventional safety system
based on electromechanical switchgear is that no separate
components are needed and the costs incurred for the
wiring and maintenance of separate components can
therefore be saved. Owing to the fast electronic switching
times, the function provides a shorter reaction time than
the conventional solution comprising electromechanical
components.
Safe Torque Off (STO)
Safe Stop 1 (SS1)
The SS1 function causes a motor to stop rapidly and safely
and switches the motor to a torque-free state after it
reaches a standstill, i.e. by activating STO.
Effect
The SS1 function can safely stop the drive in accordance
with EN 60204-1, Stop Category 1. When the SS1 function
is selected, the drive brakes autonomously along a quick-
stop ramp and automatically activates the Safe Torque Off
and Safe Brake Control functions (if configured) when the
parameterized safety delay time expires.
In firmware version V4.5 and higher, an additional variant
of SS1 is available (SS1E). In this case, selection of SS1 does
not initiate autonomous braking of the drive, but starts the
safe delay timer instead. The higher-level controller remains
in control of the setpoint which must bring the drive to a
standstill within this time.
Application
The SS1 function is used when, in the event of a safety-
relevant incident, the drive must stop as quickly as possible
followed by transition into the STO state (e.g. EMERGENCY
STOP). It is thus used to bring large centrifugal masses to
a stop as quickly as possible for the safety of the operating
personnel, or to brake motors at high speeds as quickly
as possible. Typical applications include saws, grinding
machine spindles, centrifuges, winders, and storage and
retrieval systems.
Customer benefits
The targeted stopping of a drive by means of SS1 reduces
the risk of danger, increases the productivity of a machine,
and allows the safety clearances in a machine to be reduced.
The principle is to bring the drive actively to a standstill as
opposed to using the STO function on its own. Complex
mechanical brakes that are susceptible to wear are not
normally required to brake the motor.
Safe Stop 1 (SS1)
Safety Integrated – Description of functions
STO
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STO